A process of forming a multilayer coating film by successively coating with an undercoat paint (such as an electrodeposition paint), an intermediate paint and a topcoat paint is known. Concerning the intermediate paint, however, it is necessary to coat to a thick coating film of usually more than 30 .mu.m (as a cured coating film) in order to hide the undercoat layer and to maintain the coating film properties. Therefore, it is desired to lower the coating cost of the whole multilayer coating film by making the intermediate coating film thinner without deteriorating the hiding properties and the coating film properties.
The present inventors had been conducting an intensive research to solve these problems and as a result they found that in a process of successive coatings by an undercoat paint, an intermediate paint and a topcoat paint it is possible to make the intermediate coating film thinner with improved undercoat hiding properties and chipping resistance of the intermediate coating film and, in addition, with improved smoothness of the topcoat surface by using a thermocurable paint containing both components of aluminium powder and titanium oxide pigment as the intermediate paint and by coating a topcoat paint after curing of the intermediate coating film, and completed the present invention.